The present invention relates to a surface-combustion radiant burner comprising a porous element for use in radiant appliances in which gaseous fuel, such as natural gas and LPG are used as fuel.
When in a surface-combustion radiant burner an air/gas mixture is forced through an element having a large number of pores and is ignited near the downstream side of the element, the burning gases, in addition to producing heat by combustion, also produce a high proportion of radiant heat from the burner surface in the form of infrared rays. Heat-treatment processes continue to need faster heating rates and precision in heat application. In this connection surface-combustion radiant burners may be suitably used because of the possibilities of high heat transfer rates, silent operation and stable combustion over a range of gas/oxidant ratios from about 60 percent to 180 percent of the stoichiometric ratio.
The commercially available radiant burners normally have porous media formed of granulated ceramic material or ceramic fibers. A major requirement for radiant burners is the ability to withstand thermal shock and severe oxidative and corrosive conditions in a high temperature environment and under surface combustion conditions. Ceramic materials are known to have good oxidation and corrosion stabilities. Further advantages of ceramic materials or radiant heating appliances are the possibility of high heat transfer rates, silent operation and stable combustion over a wide range of fuel/oxidant ratios. However, limiting conditions are the restricted ability of ceramics to withstand very high thermal and mechanical stresses which may be imposed. Another difficulty with ceramic elements is that they are fragile and easily broken.
To overcome the above disadvantages encountered with ceramic materials, it has already been proposed to use metals for radiant burners. Wholly metallic radiant burners have a great advantage over ceramic burners in that they are very robust and have a better thermal shock-resistance. The available metals such as austenitic and ferritic stainless steels, however, oxidize rapidly under surface combustion conditions where temperatures greater than 1200 K are encountered. Oxidation induced corrosion causes the resistance to flow of the porous elements to increase and this severely limits its useful life. The known metallic radiant burners are therefore limited to application under rather moderate temperature conditions.
The object of the present invention is to provide an improved surface combustion radiant burner with a metallic porous element having a high oxidation and corrosion stability under high temperature surface combustion conditions.